The present invention relates to a bearing comprising a polymer, wherein the ferrous base material is coated with a layer of bronze alloy, on which a layer is deposited by sputtering, which in turn receives a polymeric sliding layer provided, among other elements, with a soft metal alloy, wherein the primary layer and the sputtered layer can be associated by means of a bonding layer.
Taking into account the growing demands of the automobile industry, especially as far as environmental questions are concerned, new requirements have arisen, which are reflected directly on the components of internal combustion engines. Some of the pieces that naturally undergo this effect are bearings and, as a result, bronze bearings.
Numerous developments have emerged with a view to improve corrosion resistance, friction coefficient and anti-gripping properties. On the other hand, the increase in work pressures of internal combustion engines make it difficult to succeed in such attempts by causing the bearings to wear early. It should be noted that the future does not hold in store any ease for this field of actuation; suffice it to observe that more powerful are required, which can reach higher rotation regimes, are more efficient and consume less fuel.
Naturally, in the face of the new demands, new materials will be necessary, since the known ones are the same that limit the performance of internal combustion engines today.
In addition, due to the growing demands on internal combustion engines, one has used lubricating oils having reduced viscosity with a view to reduce friction. This represents a particularly serious problem for bearings on an internal combustion engine, because at high speeds the oil layer around the bearing undergoes a thinning phenomenon, causing greater contact between metallic elements, which leads to a premature wear of the bearing.
With a view to try and solve the problems indicated, one has developed multiple-layer bronze bearings. The construction in layers usually comprises a resistant base material such as steel coated with a soft-metal alloy and at least one sliding layer, which will keep contact with the film of lubricating oil. These layers are generally applied by means of a coating of rolling material first adhered to the support and at least one additional layer of a rolling material adhered to the surface of the rolling material in the first place. The outer surface of the latter rolling material forms the real sliding surface that interacts with the axle.
It is relevant to note that the importance of the layers is not limited exclusively to the sliding layer. Instead, the function of the layers is found through interaction between them, each having a specific role in the performance of the bearing, as well as a function with regard to the adjacent layer. Moreover, as a rule, bearings are provided with more than one layer for the sake of longevity thereof. Thus, when a sliding layer is worn, another layer will come in contact with the oil film from then on, acting as a sliding layer or wear layer. In these circumstances, the layer applied onto the base material (primary layer) has the objective of providing resistance to gripping and actuating with reasonable performance as a sliding layer too.
Typically, the primary layer has inferior performance in both adapting minor offsetting between the bearing surface and the axle surface, and in capability of adapting countering the particles present in the oil film that would cause scratches or wear of the surfaces.
In view of this concern, one has proposed solutions constituted by a number of layers, each having a defined function for improving the tribologic output, in with a view to prevent the problems mentioned before.
One of these solutions can be exemplified with the deposition of aluminum and tin by the sputtering process onto a primary layer of material of the bearing. Such bearings have, as the main characteristic, the advantage of standing high loads. Anyway, the drawback is that the layer deposited has low sensitiveness to great variations or discontinuities in the oil film, resulting in potential degradation of the bearing and impairing the performance in the long run, thus impairing the functioning of the engine or even leading to failure thereof.
Patent application GB2465852 describes a polymeric sliding layer with a view to improve the performance of a bearing for use on an engine that operates under heavy-duty conditions. The polymeric layer described contains additives that reduce friction, being constituted by a matrix containing 5% to 15% by volume of metallic powder, preferably chosen from the group consisting of aluminum, copper, silver, tungsten and stainless steel; 1% to 15% by volume of fluoropolymer, preferably PTFE or FEP, the balance being a polyamide-imide resin.
It should be noted that the great characteristic of this polymeric sliding layer is that it does not undergo wear and remains on the bushing throughout the useful life thereof, providing it with a load capacity higher than that of conventional bushings. Such an effect generally has superior performance when the aluminum powder is used. Anyway, the bearing disclosed by this British document exhibits a disadvantage. The absence of a layer deposited by the sputtering process reduces the load capacity of the bearing. If this disadvantage is coupled to the growing demand for more charged internal combustion engines, then the application of this bearing will certainly be limited.
Another bearing known from the prior art is described in U.S. Pat. No. 7,541,086. Unlike the above-cited document, the presently disclosed bearing has a constructive configuration provided with a layer deposited by the sputtering process. The mere existence of this deposited layer already indicates that the bearing has higher load capacity and resistance to wear. Anyway, the novelty of this document does not lie in this fact, since bearings provide with layers deposited by the sputtering process are already known since long ago.
Thus, the bearing presented by this patent rests on a fundamental point. The creation of a sliding polymeric layer applied onto the deposited layer. It should be noted, however, that this polymeric sliding layer has nothing to do with the polymeric sliding layer of document GB 2465852, since this is a polymeric sacrifice layer provided with molybdenum disulfate which, as it is known, is an excellent lubricant.
However, the chemical configuration of the polymer was not designed so that it will last throughout the useful life of the bearing. Instead, the objective is that this polymeric layer will wear during the first hours of operation, so that the molybdenum disulfate will be released from the polymer to be impregnated in the deposited layer.
As a result, after a few hours of operation, the bearing described in this document has a constructive configuration equivalent to that of the prior art, that is, it behaves as a bearing whose main element that exhibits performance in its durability is the sputtered sliding layer. Consequently, this bearing cannot guarantee high load capacity, although it exhibits good resistance to gripping.
These two documents synthesize the great difficulty of obtaining a bearing capable of providing a balance point between resistance to gripping and high load capacity. Naturally, these characteristics have always been sought, but not yet materialized, even in the present applications, let alone in future demands which the automotive industry has been stating to be fundamental so vehemently.
A reason for this lies in the limit values usually encountered by prior-art bearings. In this regard, one should note that the value of load capacity of a bearing provided with a sputtered sliding layer usually ranges from 100 MPa to 120 MPa, the usual gripping load ranging from 50 MPa to 60 MPa. In an attempt to improve the resistance to gripping, bimetallic bearings with polymer may achieve values on the order of 85 MPa to 90 MPa. Anyway, the usual load capacity is of about 70 MPa to 80 MPa. Such values demonstrate clearly the difficulty in achieving an improvement of one of the properties, without there being a significant impairment of the other.
Naturally, harmonizing technologies is something possible, but often made unfeasible by the high cost of development and industrial production. In this regard, one has always tried to achieve more durable bearings by merely modifying the layers, rather than combining layers.
Thus, it is necessary to find a bearing that manages to combine the characteristics responsible for the durability of the bearing, so that the latter will have a load capacity value equal to or higher than 120 MPa and a value for the gripping load higher than 85 MPa.